Process for manufacturing a tyre and toroidal support for carrying out said process

ABSTRACT

A process for manufacturing a tyre includes providing an elastomeric layer on an outer surface of a toroidal support, manufacturing the tyre on the toroidal support provided with the elastomeric layer, introducing the tyre supported on the toroidal support into a moulding cavity, introducing a fluid under pressure into a space defined between the toroidal support and an inner surface of the tyre in order to press an outer surface of the tyre against walls of the moulding cavity, and curing the tyre. The elastomeric layer forms an inner circumferential surface of the tyre. The process further includes causing an electrical current to flow in at least one heating element provided to the outer surface of the toroidal support so as to obtain at least partial precuring of the elastomeric layer. A toroidal support for carrying out the process is also disclosed.

The present invention relates to a process for manufacturing a tyre. Inparticular, the present invention relates to a process for manufacturinga tyre comprising the steps of producing and assembling the tyrestructural elements on a toroidal support and precuring the innersurface of the green tyre by heating the outer surface of said toroidalsupport.

Furthermore, the present invention relates to a toroidal support to beused in a process for manufacturing a tyre, the outer surface of saidtoroidal support being heated during the precuring step of saidmanufacturing process.

In the present description, the term “green tyre” is used to indicatethe product which is obtained upon assembling tyre structural elementswhich include an elastomeric material in an uncured state.

Furthermore, in the present description the term “elastomeric material”is used to indicate a composition comprising at least one elastomericpolymer and at least one reinforcing filler. Said composition preferablyalso includes additives such as crosslinking agents and/or plasticizers.

Moreover, in the present description, the term “sinner surface” of thetyre is used to indicate the innermost surface of the tyre which, whenthe tyre is cured and operatively mounted on a wheel rim, comes intocontact with the inflating fluid of the tyre.

The manufacturing process according to the present invention comprisesthe step of manufacturing a green tyre by consecutively producing andassembling together on a toroidal support the tyre structural elements,as described, for instance, in the European Patent Application N^(o)928,680 in the name of the same Applicant.

The manufacturing process further comprises the successive steps ofmoulding the green tyre, so as to confer to the latter a desired treadpattern, and of curing the green tyre, so as to confer to the latter adesired geometrical conformation which is obtained by curing theelastomer material forming the tyre itself.

The moulding and curing steps of the green tyre are carried out byintroducing the green tyre into a moulding cavity defined within avulcanization mould, whose shape matches the shape of the outer surfaceof the tyre to be obtained, and by admitting a fluid under pressure intoa diffusion interspace created between the inner surface of said greentyre.and said toroidal support.

Such a manufacturing process is described, for instance, in the EuropeanPatent Application N^(o) 976,533 in the name of the same Applicant,according to which, during the pressing of the raw elastomer materialagainst the walls of the moulding cavity, a radial expansion. is imposedto the tyre by effect of the pressurized-fluid admission. Thepressurized-fluid admission is preferably carried out by means offeeding channels formed in the toroidal support and terminating at theouter surface of the latter. During the pressurized-fluid admission, thetyre is sealingly engaged at its circumferential inner edges, betweenthe walls of the moulding cavity and the outer surface of the toroidalsupport, so as to delimit the diffusion interspace at thecircumferential inner edges of the tyre itself. Advantageously, the heatamount which is necessary for curing the green tyre is provided to thelatter through the walls of the moulding cavity and by means of aheating fluid which is introduced into the diffusion interspace.Preferably said heating fluid is the fluid under pressure used forcarrying out the pressing step or is at least part of said fluid underpressure.

Therefore, in accordance with such a process, the manufacturing of atyre is carried out in the absence of a vulcanization bladder which iscommonly employed in conventional processes. The bladder is generallymade of rubber and is inflated with steam and/or a high-pressure heatedfluid and inserted into the green tyre, enclosed in the moulding cavity,in order to conveniently press the tyre against the walls of themoulding cavity and to provide the tyre with the desired geometricconformation as a result of the cross-linking process to which theelastomer material forming the tyre itself is submitted.

However, in processes without a vulcanization bladder as describedabove, the fluid under pressure directly comes into contact with theinner surface of the green tyre causing a plurality of inconveniencesdue to permeation of the fluid itself into the structure of the tyre notyet, vulcanized. For instance, separations between adjacent elastomericlayers or between the elastomeric material and the metallic or textilereinforcing structures may occur, or even corrosion phenomena in themetallic reinforcing materials may be unadvantageously promoted.

In order to avoid the inconveniences mentioned above, European PatentApplication N^(o) 976,534, in the name of the Applicant, describes atyre manufacturing process comprising the step of associating at leastone layer of precured elastomeric material with the inner surface of thegreen tyre for preventing the permeation of the fluid under pressureinto the inside of the green tyre itself. Said precured layer issuitable for obtaining a sufficient mechanical strength to diffusion andpenetration of the fluid under pressure and, at the same time, a highfatigue strength, in particular during the moulding step of the tyre inorder to avoid formation of fissures and cracks. Therefore, according tosaid European Patent Application the manufacturing process comprises thesteps of forming at least one layer of raw elastomeric material on theouter surface of the toroidal support, so that the successivemanufacturing of the green tyre is carried out on the toroidal supportcarrying said layer of raw elastomeric material, and of precuring saidlayer before introducing the green tyre into the vulcanization mould.Said precuring step is carried out by supplying heat to said layerthrough the toroidal support. Preferably, heating of the toroidalsupport is achieved thanks to the fact that the toroidal support comesfrom a previous moulding and vulcanization cycle or by means of infraredrays or equivalent means, such as electric resistors arranged in thetoroidal support itself.

European Patent Application N^(o) 1,075,929 discloses a process formanufacturing a tyre according to which a rigid toroidal support is usedas support on which the green tyre is manufactured and as moulding meansfor moulding the radial inner surface of the tyre. Said European PatentApplication is focused to the problem of providing a toroidal supportwhich is mechanically resistant, without compromising the easiness ofassembling/disassembling the different parts of said support, good heatconductor, in order to supply heat to the green tyre for the curingthereof, and suitably light to be easily transferred along theproduction plant. According to said document, the toroidal supportconsists of a plurality of sectors, each sector being formed by twodistinct portions: a principal portion, whose radially outer surfaceregion forms the inner circumferential surface of the tyre, and acoupling portion, positioned radially internal to said principal portionand integral thereto, which is associated to a coupling device thatassembles together the plurality of sectors to form the toroidalsupport. Furthermore, according to said document the principal part ofeach sector is moulded in a thermally conductive material (e.g., analuminum alloy) and incorporates an electrical resistance for providingheat to the green tyre during the curing step. In a further embodiment,said electrical resistance can be placed in a bored housing within saidprincipal part or can be fixed to the radially internal surface of saidprincipal part.

Document JP 11-320,567 discloses a toroidal support on which a greentyre is manufactured, each sector of said support being contacted, incorrespondence of the inner circumferential surface thereof, with acircular segment provided with resistor heaters so that a heat amount issupplied to the outer circumferential surface of the toroidal supportfrom the inner circumferential surface thereof for curing the greentyre. The plurality of circular segments is arranged along the throughhole of a cam of the toroidal support so that the circular segments, andthus the respective resistor heaters, are placed in the working positionand can be retracted at the end of the curing step.

In a process for manufacturing a tyre wherein the green tyre isassembled on a toroidal support and the curing step is carried out inthe absence of a vulcanization bladder, a plurality of drawbacks occursdue to the fluid under pressure contacting the inner surface of thegreen tyre.

The technical solution disclosed in European Patent Application N^(o)976,534, i.e. precuring the layer of raw elastomeric material formingthe inner circumferential surface of the tyre, advantageously avoids theoccurring of said drawbacks. Furthermore, precuring said elastomericlayer, commonly referred to as “liner”, i.e. the elastomeric layer whichis suitable for ensuring the retention of the tyre inflating fluid, isparticularly advantageous also during the conformation of the tyre sincethe precured liner is provided with high mechanical resistance. On thecontrary, in the case an uncured elastomeric layer is present, themechanical resistance thereof is not substantially the same in eachpoint of said layer so that, during the admission of fluid underpressure, the surface of said layer can react differently from point topoint and a uniform conformation of the tyre is prevented. Said aspectis particularly true in the case the uncured elastomeric layer isobtained by assembling together a plurality of elastomeric strips asdescribed, for instance, in European Patent Application N^(o) 928,680.Moreover, since the fluid under pressure exiting from the feedingchannels provided within the toroidal support does not uniformly impactonto the liner surface, in the case the latter is uncured said fluidcreates the formation of disuniformities on the inner circumferentialsurface of the tyre as well as of areas of different colours, factswhich cause the tyre not to be accepted from an aesthetic point of view.According to European Patent Application N^(o) 976,534, the precuring ofthe inner circumferential surface of a green tyre is carried out bysupplying heat thereto through a toroidal support which is heated in allits constitutive parts thanks to its use in a previous moulding andvulcanization cycle or by means of infrared rays or any equivalentmeans, such as electric resistors.

According to European Patent Application N^(o) 1,075,929 the whole bodyof the toroidal support is heated and the latter is used as a heatdiffuser. In order to achieve such a result, the principal part of eachsector of the toroidal support is provided with an electrical resistanceincorporated within said principal part, which is made of thermallyconductive material, so that a heat amount is supplied to the green tyreduring vulcanization through the toroidal support. According to saiddocument the electric resistance causes the heating of the principalpart of each sector as well as of the anchoring part of each sector,which is integral with said principal part, so that the whole body ofthe toroidal support is heated.

Furthermore, document JP 11-320,567 discloses a technical solutionaccording to which the whole body of the toroidal support is heated.

Therefore, all the technical solutions described in the prior artdocuments cited above are directed to a complete heating of the wholebody of the toroidal support in order to transmit a heat amount to agreen tyre's structural component.

The Applicant has perceived that, in order to precure the innercircumferential surface of a green tyre, it is not necessary to heat thewhole body of the toroidal support. The Applicant, in fact, has notedthat heating the whole body of the toroidal support is energy and timeconsuming, and decreases the average life of the toroidal supportmaterial which is subjected to thermal fatigue damages.

Therefore, the Applicant has found that, in order to carry out saidprecuring step, a local heating of the outer surface of the toroidalsupport can be performed.

In other words, the Applicant has found that the toroidal support can beprovided with at least a heating element which is able to transmit asuitable heat amount to the inner circumferential surface of the greentyre to be precured and to ensure that no substantial heat amount istransmitted inwardly the toroidal support, i.e. far from said innercircumferential surface of the green tyre to be precured.

To achieve such a result, the Applicant has found that the toroidalsupport can be provided with a heating element which comprises, in aradial direction from the inside towards the outside of said heatingelement, a thermally insulating layer and an electrically resistivecircuit so that a major amount of the heat produced by said circuit,when a current is made to flow therein, is transmitted to theelastomeric layer to be precured. In fact, the presence of saidthermally insulating layer limits the heat produced by said circuit tobe dissipated inside of the toroidal support.

Furthermore, the Applicant has found that a heating element comprisingat least one thermally insulating layer and an electrically resistivecircuit allows a uniform heating of the toroidal support outer surfaceso that the precuring of the inner elastomeric layer of a tyre ishomogeneously performed.

In a first aspect the present invention relates to a process formanufacturing a tyre comprising the steps of:

-   -   providing an elastomeric layer on an outer surface of a toroidal        support having a shape substantially matching the shape of the        inner surface of said tyre, said elastomeric layer forming the        inner circumferential surface of a green tyre;    -   manufacturing said green tyre on said toroidal support provided        with said elastomeric layer;    -   introducing said green tyre supported on said toroidal support        into a moulding cavity having walls the shape of which matches        the shape of an outer surface of the tyre;    -   introducing a fluid under pressure into the space defined        between the inner surface of said green tyre and said toroidal        support in order to press the outer surface of said green tyre        against the walls of said moulding cavity, and    -   curing said green tyre,

wherein said process further comprises the step of causing an electricalcurrent to flow in at least a heating element provided to the outersurface of said toroidal support so as to obtain an at least partialprecuring of said elastomeric layer.

According to a preferred embodiment, the step of causing an electricalcurrent to flow in at least one heating element provided to the outersurface of said toroidal support is carried out before the step ofintroducing the fluid under pressure.

The Applicant has noted that locally heating the outer surface of thetoroidal support is particularly advantageous in terms of: a) energysaving, since only a limited portion of the toroidal support is heated;b) increased average life of the toroidal support material, since thelatter is not subjected to thermal fatigue damages, and c) time saving,since the desired precuring temperature can be quickly reached due tothe limited area of the toroidal support to be heated. Furthermore, inthe recent tyre manufacturing processes, according to which a tyre isformed directly on a toroidal support by overlaying axially adjacentand/or radially superimposed turns of at least a semi-finishedelementary product of appropriate dimensions wound onto said support,the precuring step of the inner circumferential surface of a green tyrehas to be carried out in a time compatible with the manufacturing timeof the tyre.

Moreover, according to the present invention the toroidal support iseffectively heated so that the external surface thereof quickly reachesthe desired temperature and said temperature is as uniformly distributedas possible on said external surface.

According to a first embodiment, the heating of the toroidal support iscarried out when the elastomeric layer is completed and supported on theouter surface of said support. Said elastomeric layer can be provided tothe toroidal support in the form of a sheet, in accordance withconventional tyre manufacturing techniques wherein each elastomericcomponent is extruded in its final shape and stored ready to be used onthe manufacturing machines, or in the form of a profiled strip ofelastomeric material, in accordance with more recent tyre manufacturingprocesses, as for example shown in European patent applicationEP-928,680.

According to a further embodiment of the present invention, the heatingof the toroidal support is carried out at the end of the step ofmanufacturing the green tyre on the toroidal support. In other words,according to said embodiment, the tyre manufacturing process comprisesthe step of producing the green tyre by forming and/or assemblingtogether the tyre structural elements and subsequently precuring theinner circumferential surface of the tyre before introducing the latterinto the moulding cavity within which moulding and curing are performed.An example of a tyre manufacturing process is described in theabovementioned European Patent Application EP-928,680 according to whicha limited number of semi-finished elementary products are fed onto atoroidal support which is conveyed, preferably by a robotized system,between a plurality of stations, at each of which a predeterminedtyre-manufacturing step is carried out in automated sequences. Byoverlaying said semi-finished elementary products on said toroidalsupport in adjacent turns, the entire structure of the green tyre can beobtained.

According to a further embodiment of the present invention, the heatingof the toroidal support is carried out before the step of providing theelastomeric layer on the outer surface of the toroidal support. In otherwords, at the beginning of a manufacturing cycle of a tyre, the toroidalsupport is suitably heated to a predetermined temperature by means ofthe heating element according to the present invention and subsequentlyan elastomeric layer (e.g. the liner) is provided to the outer surfaceof the toroidal support. In such a way the precuring of said elastomericlayer starts during the deposition thereof on the heated toroidalsupport. Furthermore, according to said further embodiment, bypreheating the toroidal support before manufacturing the tyre anymoisture, possibly present on the support outer surface and due, forexample, to a previous tyre manufacturing cycle, can be avoided.

According to a further embodiment of the present invention, the heatingof the toroidal support is carried out also during the curing step inaddition to the beat which is provided by the vulcanization fluid and bythe walls of the moulding cavity. In fact generally, since the tyre tobe vulcanized is positioned inside of the moulding cavity with itssidewalls substantially parallel to the base of the vulcanizer, thecondensate that forms during the .curing step accumulates incorrespondence of the lower sidewall of the tyre so that said lowesidewall reaches a temperature, and thus a curing degree, lower thanthat of the upper sidewall. In order to avoid such a drawback, accordingto the present invention a locally heat distribution of the toroidalsupport can be carried out so that the lower sidewall can be heated morethat the upper one.

According to a further embodiment of the present invention, at least aportion of the outer surface of the toroidal support is selectivelyheated.

In a further aspect the present invention relates to a toroidal supportfor manufacturing a green tyre thereupon, said support comprising aplurality of circumferential segments defining the outer surface of saidtoroidal support, said outer surface having a shape which substantiallymatches the shape of the inner surface of said green tyre, wherein saidtoroidal support further comprises at least a heating element coveringat least a portion of the outer surface of said toroidal support, saidheating element comprising, in a radial direction from the insidetowards the outside of said heating element, a thermally insulatinglayer and an electrically resistive circuit.

According to a preferred embodiment of the present invention, theheating element further comprises a protective layer positioned radiallyexternal to the electrically resistive circuit. Said protective layer,which comes into contact with the elastomeric material to be precured,is made of electrically insulating material. First of all saidprotective layer has the function of preventing the technical staffoperating on the toroidal support from inadvertently touching theelectrically resistive circuit. Furthermore, said protective layer isrequested to be sufficiently tacky to allow a correct manufacturing ofthe tyre structural elements thereupon as well as to be provided withsufficient anti-sticking properties so that said elastomeric material iseasily detachable from the toroidal support.

According to a preferred embodiment, the toroidal support comprises aplurality of circumferential segments defining the outer surface of thetoroidal support, each circumferential segment being provided with aheating element.

Alternatively, a number of circumferential segments are provided with aheating element, while the remaining circumferential segments are devoidof a heating element so that a locally distributed heating can beperformed.

According to a further embodiment, each circumferential segment isobtained by assembling together at least two distinct elements. Forinstance, one element can correspond to the tyre sidewall and anotherone can correspond to the tread band or a portion thereof. Therefore,according to said embodiment, some of the elements forming eachcircumferential segment are provided with the heating element so thatspecific portions of the tyre can be selectively heated.

According to a further embodiment, the plurality of circumferentialsegments is provided with a heating element, but only few of them areselectively heated. In other words, by making the electrical current toflow within selected electrically resistive circuits of the heatingelements, predetermined circumferential segeents are caused to heat sothat a locally distributed heating of the outer surface of the toroidalsupport can be performed.

According to a further embodiment of the present invention, at least anumber of the cirumferential segments of the toroidal support isprovided with a heating element having at least two electrircallyresistive circuits. In other words, according to said embodiment eachcircumferential segment is divided into at least two distinct portionseach provided with an electrically resistive circuit connected to acurrent generator. In such a way it is possible to make the electricalcurrent flowing into at least one of said electrically resistivecircuits so that each circumferential segment can be provided withdifferently heated portions thereof and a locally distributed heating ofthe outer surface of the toroidal support can be performed.

According to a further embodiment, the circumferential segments of atoroidal support are provided with electrically resistive circuitshaving different geometrical configuration so that a locally distributedheating of the outer surface of the toroidal support can be performed.For example, said circumferential segments can be provided withelectrically resistive circuits having different longitudinaldevelopment as well as different density or width of the heatingbranches of said circuit.

According to a further embodiment, in order to obtain a locallydistributed heating of the outer surface of the toroidal support, in thecase each circumferential segment is provided with at least two distinctelectrically resistive circuits, the latter present the same density ofthe heating branches but a different electrical current intensity iscaused to flow within said at least two distinct electrically resistivecircuits.

According to a further embodiment, in order to obtain a locallydistributed heating of the outer surface of the toroidal support, theelectrically resistive circuit presents a variation of the density ofthe heating branches so that the same electrical current intensitycreates two zones of the circumferential segment which are differentlyheated.

According to a further embodiment, in order to obtain a locallydistributed heating of the outer surface of the toroidal support, in thecase each circumferential segment is provided with at least two distinctelectrically resistive circuits, the latter present a different densityof the heating branches but the same electrical current intensity iscaused to flow within said at least two distinct electrically resistivecircuits.

Furthermore, suitable electrical current conditions can be selected suchas, for instance, direct current, alternate current, pulsanting current,waveform current (e.g. square wave).

Furthermore, the electrical current intensity can be advantageouslycontrolled and, if necessary, modified by a rectifier (controller) whichacts on the current generator in the case said electrical currentintensity deviates from a set value or from a predetermined curve ofsaid electrical cur-rent intensity.

Further characteristics and advantages of the present invention will beillustrated by the following description of some preferred embodiments.

The following description makes reference to the accompanying drawings,in which:

FIG. 1 schematically shows a diametrical section of an apparatus formanufacturing a tyre in accordance with the invention during the step ofloading a tyre into a mould shown in an open condition;

FIG. 2 shows a perspective view of a heating element associated to ametallic substrate in the form of a plate according to an embodiment ofthe present invention;

FIGS. 4 to 6 show the steps of different methods for providing thecircumferential segments of a toroidal support with a heating element inaccordance with the present invention, and

FIG. 7 shows a graphic representation of the temperature increase vs.time for a heating element according to the invention.

A tyre usually comprises a carcass structure having at least one carcassply of toroidal shape, associated by its circumferential edges to a pairof annular reinforcing structures or “bead cores”, each reinforcingstructure being positioned in the finished tyre in an area usually knownas the “bead” which ensures the fitting of the tyre into the respectivefitting rim. In a position radially external to the abovementionedcarcass ply is provided a belt structure, comprising one or more beltstrips laid on top of each other, and a tread band is laid radiallyexternal to the abovementioned belt structure. In the vulcanized tyresaid tread band it provided with a suitable tread pattern moulded intoit during the vulcanizing process. Furthermore, two side walls arelaterally placed on opposite sides of the abovementioned carcassstructure. The carcass structure is preferably covered radially on theinside by a layer of elastomeric material known as the “liner” to ensurethat the tyre is airtight under running conditions.

With reference to FIG. 1, an apparatus for manufacturing a tyre isgenerally identified by reference sign 1.

Apparatus 1 comprises a vulcanization mould 2 associated with avulcanization press 3, only diagrammatically shown in that it can bemade in any convenient manner as conceived by a person skilled in theart. The vulcanization mould 2 is provided with lower 2 a and upper 2 bmould halves that are movable relative to each other between an opencondition (in which they are mutually spaced apart as shown in FIG. 1)and a closed position (in which they are disposed mutually close to eachother for the purpose of forming a moulding cavity). The lower 2 a andupper 2 b mould halves are provided with lower 4 a and upper 4 b cheeksrespectively, and a crown of lower 5 a and upper 5 b sectors in order toreproduce the geometric conformation of the outer surface 7 a of a tyre7 to be obtained. In more detail, cheeks 4 a, 4 b are intended forforming the outer surfaces of the opposite sidewalls 8 of tyre 7,whereas sectors 5 a, 5 b are intended for forming the so-called treadband 9 of the tyre itself, creating a series of cuts and longitudinaland/or transverse grooves therein, suitably disposed according to adesired tread patterns.

Apparatus 1 is further provided with at least one toroidal support 10having an outer surface substantially reproducing the shape of an innersurface of tyre 7. The toroidal support 10 is conveniently made up of acollapsible drum comprising centripetally movable circumferentialsegments for dismantling the toroidal support itself and enabling easyremoval of the same from tyre 7, at the end of the manufacturingprocess. A green tyre is disposed on the toroidal support 10 before thelatter is fitted, together with the tyre itself, into the vulcanizationmould 2 arranged in an open condition. In particular, engagement of tyre7 on the toroidal support 10 can be conveniently obtained by directlymanufacturing the tyre on the support itself. In this way the toroidalsupport 10 is advantageously utilized as a rigid outline for formingand/or deposition of the different structural elements, such as carcassplies, bead-reinforcing structures, belt strips, sidewalls, and treadband for example, which structural elements cooperate in forming thetyre itself.

The toroidal support 10 is preferably provided with at least onecentering shank 11 to be engaged in a centering seat 12 arranged inmould 2, for establishing a precise positioning of the toroidal supportitself and the tyre 7 carried thereon, within the moulding cavity. Inthe embodiment shown in FIG. 1, two centering shanks 11 are provided tothe toroidal support 10 extending from opposite sides thereof.

At the moment that mould 2 is closed, the waIls of the moulding cavityremain at a certain distance from the outer surface of tyre 7, inparticular at the tread band 9 of the latter. During this step, thetread band 9 can in any case be partly penetrated by the raised portionsarranged on sectors 5 a, 5 b so as to define said tread pattern.Furthermore, at the moment that mould 2 is closed, each of the innercircumferential edges 8 a of tyre 7 is sealingly engaged between theinner circumferential portions of the toroidal support 10 and innercircumferential portions of the lower 4 a and upper 4 b cheeks. Tyre 7will remain sealingly engaged in the mould in the above described manneruntil the moment that, at the end of the moulding and curing cycle, themould itself will be brought again to its open condition. When mouldclosure has been completed, tyre 7 is submitted to a pressing step withits outer surface 7 a against the walls of the moulding cavity,concurrently with supplying of heat, so as to cause molecularcross-linking of the elastomer material forming the tyre itself andconsequent geometric and structural stabilization of the latter. Forthis purpose, apparatus 1 is provided with pressing means comprising atleast one primary duct 13 opening into one of the centering seats 12 forsending a fluid under pressure to at least one connecting duct 14 formedalong at least one of the centering shanks 11, preferably coaxiallytherewith. The connecting duct 14 terminates, for example throughappropriate branches 15 radially formed in the toroidal support 10, atan annular chamber 16 provided internally of the toroidal supportitself. Extending from the annular chamber 16, through the toroidalsupport 10, is a plurality of channels 17 for feeding said fluid underpressure, which open into the outer surface 10 a of the toroidal supportitself and are suitably distributed over the circumferential extensionof said support. The pressurized fluid fed from the primary duct 13reaches the feeding channels 17 via the connecting duct 14, the radialbranches 15 and the annular chamber 16, then opening onto the outersurface 10 a of the toroidal support 10. The pressurized fluid is thusadmitted to a diffusion interspace created between the outer surface 10a of the toroidal support 10 and the inner surface 7 b of tyre 7, saiddiffusion interspace is directly created following an expansion of tyre7 caused by effect of the thrust exerted by the pressurized fluid.

With reference to FIG. 2, a heating element 20 is shown associated to ametallic substrate 21 in the form of a plate. According to theembodiment shown in FIG. 2, heating element 20 comprises a thermallyinsulating layer 22, covering the outer surface of the metallicsubstrate 21, and an electrically resistive circuit 23 associated tosaid thermally insulating layer 22.

FIG. 2 shows a plurality of heating branches 23 a forming saidelectrically resistive circuit 23 which are flown by an electric currentfed by a current generator (not shown). According to the embodiment ofFIG. 2, the greatest part of the surface area of the metallic substrate21 is covered by said heating branches 23 a so that a fast and uniformdistribution of the heat produced by the flowing of the electric currentwithin the electrically resistive circuit 23 can be obtained on theouter surface of said substrate 21. Therefore, the embodiment of FIG. 2shows an electrically resistive circuit 23 having a very high density ofheating branches 23 a. Nevertheless, heating elements 20 (not shown)provided with a density of the heating branches 23 a lower than that ofFIG. 2 can be provided if needed, as well as heating elements 20 (notshown) presenting at least two portions provided with different densityof said heating branches 23 a (e.g. a first portion with high densityand a second portion with low density of said heating branches). It canbe pointed out that, under the same electrical current provided by thecurrent generator, by varying the density of the heating branches ofsaid electrically resistive circuit, i.e. the design thereof, avariation of the heating rate can be obtained.

As mentioned above, the thermally insulating layer 22 of the heatingelement 20 is provided so that the metallic substrate 21, i.e. thecircumferential segments of the toroidal support, is thermallyinsulated.

Preferably, said thermally insulating layer 22 is made of a ceramicmaterial. Preferably said ceramic material is selected in the groupcomprising: a mixture of Zirconium dioxide and Magnesium oxide(ZrO₂—MgO), Aluminum oxide (Al₂O₃), a mixture of Aluminum oxide andTitanium bioxide (Al₂O₃—TiO₂), a mixture of Zirconium dioxide andTitanium bioxide (ZrO₂—TiO₂).

Preferably, said thermally insulating layer 22 is applied by using aplasma-spray technique. According to said technique the materialparticles are applied by using a gas carrier which is ignited by meansof an electric arc, i.e. a plasma of ionized gases is formed by makingan inert gas (such as argon or nitrogen) to pass through a high energyelectric arc. Said plasma is used to quickly and efficiently melt thematerial to be applied which, in the molten state, is then rapidlyaccelerated to the surface to be coated. The high temperatures which canbe reached by using such a technique allow that materials having highmelting points (e.g. ceramics) can be processed. Furthermore, saidtechnique is very advantageous since very thin layers can be produced.

Preferably, the thickness of said thermally insulating layer 22 iscomprised between 0.02 mm and 1 mm.

Among the features of the electrically resistive circuit 23, particularcare has to be paid to the material to be used as well as to thethickness and the design of the electrically resistive circuit.

With regard to the material, it can be pointed out that the electricallyresistive circuit 23 needs to be made of an electrically conductivematerial so that it can be heated by the flowing of an electricalcurrent therein. Preferably, said electrically resistive circuit is madeof a metal or a metal alloy. Preferably, said material is chosen in thegroup comprising copper, tungsten, aluminum alloy. Preferably, saidmaterial is chosen to have an electrical resistivity in the range from1.7×10⁻⁶ Ω×cm to 1.1×10⁻⁴ Ω×cm.

With regard to the thickness, it can be pointed out that theelectrically resistive circuit needs to be as thin as possible in orderto maximize the heating rate to be produced. Meanwhile, it is alsonecessary that the electrically resistive circuit is thick enough to bemechanically resistant to the thermic cycles. Therefore, a compromisebetween said two different requirements has to be reached. Preferably,the thickness of said electrically resistive circuit 23 is comprisedbetween 0.01 mm and 0.5 mm.

With regard to the design, as mentioned above, the electricallyresistive circuit can present a very high density of narrow heatingbranches 23 a or a limited density of wide heating branches 23 a. In thefirst case the resistivity of the electrical circuit increases and thusit is possible to operate at lower values of electrical currentintensity; on the contrary, in the second case the electricallyresistive circuit can be easily provided to the circumferential segmentof the toroidal support, i.e. it is easier to be processed than theelectrically resistive circuit of the first case.

Suitable electrical current conditions can be selected such as, forinstance, direct current, alternate current, pulsanting current,waveform current (e.g. square wave).

In the case the same electrical current intensity is used, it can bepointed out that the best electrical performance, i.e. the highestheating rate, is obtainable when a very high density of narrow heatingbranches 23 a is provided.

Preferably, the electrically resistive circuit is applied by using aplasma-spray technique.

According to a further embodiment of the present invention, the heatingelement 30 comprises a protective layer 24 (FIGS. 3 to 6) covering theelectrically resistive circuit 23 and suitable for coming into contactwith the inner circumferential surface of a green tyre to bemanufactured on the outer surface of a toroidal support.

Preferably, said protective layer is particularly smooth so that theinner circumferential surface of the green tyre manufactured thereuponis as uniform and regular as possible.

Furthermore, said protective layer needs to be suitably thin in order toefficiently transfer the heat amount produced by the electricallyresistive circuit towards the outer surface of the toroidal support andthus towards the inner circumferential surface of the green tyre.

Preferably, said protective layer is made of a ceramic material.Preferably, said ceramic material is applied by using a plasma-spraytechnique.

According to a further embodiment, the protective layer is a coatingmade of Teflon® which advantageously presents antiadherent,autolubricant and corrosion resistance properties.

According to a further embodiment, the protective layer comprises, in aradial direction from the inside towards the outside thereof, a firstlayer made of a ceramic material and a second layer made of Teflon®.

Moreover, the ends of the electrically resistive circuit 23, coated withthe protective layer 24, are provided with respective slabs made of thesame material of the electrically resistive circuit, said slabs havingthe function of allowing a simple and quick electrical connection of theheating element with the current generator or with adjacent heatingelements.

According to an embodiment of the present invention, eachcircumferential segment is electrically connected with the adjacent onesso that only two of said segments are directly electrically connectedwith a current generator. The mutual electrical connection of saidsegments can be obtained, for instance, by providing the heating elementwith connecting pins preferably located in correspondence of the slabspresent at the ends of the electrically resistive circuit.

According to a further embodiment of the present invention, eachcircumferential segment is electrically connected to an electricalcircuit positioned within the toroidal cavity of the toroidal support.For example, a coupling element (e.g. a screw), made of the samematerial of the resistive circuit, is associated with the slabs presentat the ends of the electrically resistive circuit of eachcircumferential segment and is electrically connected (e.g. by fixing aneletrical cable to said screw) to said electrical circuit fed by thecurrent generator. Preferably, said electrical circuit is detachablefrom the toroidal support, e.g. by means of an automatic device (such asa robotized arm), before the introduction of said support within themoulding cavity.

In order to obtain a toroidal support, for manufacturing a green tyrethereupon, comprising a plurality of circumferential segments which areprovided with a heating element, comprising, in a radial direction fromthe inside towards the outside of said heating element, a protectivelayer, a thermally insulating layer and an electrically resistivecircuit in accordance with the present invention, a plurality ofproduction techniques can be used.

FIG. 3 shows the main steps (a)-(c) of a production method of acircumferential segment of a toroidal support according to theinvention.

According to said method a thermally insulating layer 22 is applied(step (a)) over the outer surface of the substrate 21, i.e. of thecircumferential segment of the toroidal support.

Subsequently (step (b)), an electrically resistive circuit 23 is formedover the thermally insulating layer 22 by using the plasma-spraytechnique.

A plasma-spray technique is advantageously used for he followingreasons. First of all, since the electrical resistance of aplasma-sprayed metal is higher than that of a laminated metal of thesame thickness (because of the presence of voids in the metal applied bythe plasma-spray technique), the electrical resistance of theelectrically resistive circuit 23 obtained with such a production methodis, under the same thickness of said circuit, higher than that of acircuit obtained from a lamination technique. Furthermore, theplasma-spray technique allows to obtain very thin (even of about 10 μm),and thus highly resistive, conductive layers. Very thin electricallyresistive circuits allow to reduce the thickness of the protectivelayers, fact which favourably enhances the heating rate provided at theouter surface of the toroidal support. Furthermore, the plasma-spraytechnique allows that pure metal particles (e.g. copper or tungsten) canbe mixed with an electrically resistive material (e.g. a ceramicmaterial) so as to increase the electrical resistance of the circuit.

Coming back to the method described with reference to FIG. 3, in orderto obtain said eletrically resistive circuit, a mask is placed over thethermally insulating layer, said mask reproducing the desiredelectrically resistive circuit to be obtained, so that at the end of theplasma-spraying process of the electrically resistive material the maskis removed and said circuit 23 is formed.

Subsequently (step c)), the protective layer 24 is finally applied overthe electrically resistive circuit 23 as described above.

According to a further embodiment of the production method describedwith reference to FIG. 3, instead of using a mask and plasma-sprayingthe material of the electrically resistive circuit over the thermallyinsulating layer covered with said mask, the design of said circuit isperformed by a gun whose movements are controlled by a computer so thata precise production of the heating branches of said circuit can becarried out.

FIG. 4 shows the main steps (a)-(c) of a further production method of acircumferential segment of a toroidal support according to theinvention.

According to said method a thermally insulating layer 22 is applied(step (a)) over the outer surface of the substrate 21, i.e. of thecircumferential segment of the toroidal support.

Subsequently (step (b)), an electrically resistive circuit, providedwith the heating branches 23 a and previously produced in the form of asheet, is associated to the thermally insulating layer 22. Theelectrically resistive circuit is prepared by starting from a sheet (forinstance of about 50 μm in thickness) which undergoes a so-calledchemical etching in order to obtain the desired thickness and refinementdegree.

Subsequently (step c)), said electrically resistive circuit 23 is coatedwith a protective layer consisting of two different layers. In details,the first protective layer 27 is a thermally insulating layer which isvery thin in corrispondence of the electrically resistive circuit 23.Said first protective layer can be made of the same material of thethermally insulating layer 22 or can be made of a different material,for instance of a different ceramic material.

Subsequently (step d)), the second protective layer 24 is finallyapplied as described above with reference to FIG. 4.

FIG. 5 shows the main steps (a)-(d) of a further production method of acircumferential segment of a toroidal support according to theinvention.

According to said method a thermally insulating layer 22 is applied(step (a)) over the outer surface of the substrate 21, i.e. of thecircumferential segment of the toroidal support.

Subsequently (step (b)), a layer 27 made of electrically resistivematerial is formed over the thermally insulating layer 22, said layer 27being subsequently cut (step (c)) to obtain the desired profile of theresistive circuit 23 provided with the heating branches 23 a.

Subsequently (step d)), the protective layer 24 is applied as describedabove.

FIG. 6 shows the main steps (a)-(e) of a further production method of acircumferential segment of a toroidal support according to theinvention. According to said method the outer surface of the substrate21, i.e. of the circumferential segment, is previously cut (step (a)) inorder to obtain a desired profile 50 suitable for embedding theelectrically resistive circuit 23. In the right cross section, the shapeof said profile 50 is preferably semi-oval or semi-circular)alternatively it can be rectangular.

Subsequently (step (b)), the thermally insulating layer 22 is appliedwithin said profile 50. Preferably, said thermally insulating layer isapplied by using a plasma-spray technique

Subsequently (step (c)), the electrically resistive circuit 23 isapplied over the thermally insulating layer 22.

Subsequently (step (d)), the outer surface of the heating element,obtained up to that point, is grinded so that the material of theelectrically resistive circuit 23 is made to be contained within saidprofile 50 so that the heating branches of said circuit are obtained.

Subsequently (step (e)), the protective layer 24 is applied as describedabove.

for further description of the invention, some illustrative examples aregiven below.

EXAMPLE 1

An aluminum plate, having dimensions of 110 mm×100 mm×10 mm, wasprovided with a heating-element according to the invention by using theproduction method previously described with reference to FIG. 3.

Said aluminum plate, i.e. the metallic substrate, was provided with afirst thermally insulating layer 22 made of the ceramic materialZrO₂—MgO and applied by plasma-spraying. Said first thermally insulatinglayer was provided with an interlayer (not shown in the figures), i.e. alayer of ZrO₂—MgO mixed with metal (in said case Aluminum) so that aconcentration gradient of said metal is provided at the interfacebetween the metallic plate and the thermally insulating layer (i.e. theceramic layer) in order to increase the thermal compatibility betweensaid metallic plate and said thermally insulating layer. Said firstthermally insulating layer, of about 250 μm in thickness, waselectrically tested by using a Unilap MIC160 equipment and an electricalresistane of about 30 GΩ was measured, said value showing that saidlayer was highly electrically resistive and thus insulating.

Subsequently, an electrically resistive circuit, previously producedfrom a thin sheet, as well as a protective layer were provided.

The dimensions of said electrically resistive circuit were of 109 mm inwidth and 90 mm in height and comprised 37 vertical heating branches 23a having a width of 1.8 mm and being spaced from each other of about 1mm. Three different resistive circuits were provided according to thedesign mentioned above: a) a resistive circuit made of copper (copperdensity equal to 2.7 g/cm³; copper electrical resitivity equal to2.8×10⁻⁶ Ω×cm; copper specific heat equal to 0.88 J/(g/K)), having athickness of about 100 μm and a weight of about 5.37 g; b) a resistivecircuit made of copper, having a thickness of about 50 μm and a weightof about 2.56 g; c) a resistive circuit made of brass (brass densityequal to 8.55 g/cm³; brass electrical resitivity equal to 6×10⁻⁶ Ω×cm;brass specific heat equal to 0.38 J/(g/K)), having a thickness of about30 μm and a weight of about 1.34 g.

Subsequently, a protective layer made of Clear Silicon (produced by RS)was applied by spraying to cover the resistive circuit. Said protectivelayer had a thickness lower than about 100 μm.

Subsequently, for each of the three heating elements mentioned above(indicated with A, B, C in Table 1 hereinbelow) the energy amountabsorbed by the electrical resistive circuit was calculated (consideringa direct electrical current of 5.3 A and 24 V) for heating the outersurface of the aluminum plate, provided with the heating element, from atemperature of 20° C. to a temperature of 140° C. The obtained values ofenergy amount corresponding to said heating elements A-C were comparedwith the energy amount absorbed by the aluminum plate for heating theouter surface thereof (i.e. not provided with the heating elementaccording to the invention) from a temperature of 20° C. to atemperature of 140° C. (aluminum density equal to 8.93 g/cm³; aluminumelectrical resitivity equal to 1.75×10⁻⁶ Ω×cm; aluminum specific heatequal to 0.39 J/(g/K)). TABLE 1 Energy amount Heating element (kJ) A0.24 B 0.12 C 0.06 Aluminum plate 28.5

The data reported in Table 1 show that a remarkable energy saving can beobtained by providing the toroidal support with the heating systemaccording to the present invention when compared with traditionalheating of the whole body of the toroidal support.

Furthermore, FIG. 7 shows that, by electrically connecting a currentgenerator (5.3 A and 24 V) to the heating element C, the outer surfaceof the metallic support (aluminum plate) reaches a temperature of 166°C. (starting from a room temperature of 23.2° C.) in about 5 minutes,i.e. in a very short period of time, while the heating elements A and Brequire a period of time which is nearly twice than C.

EXAMPLE 2

Five samples were obtained (as indicated in Table 2 hereinbelow) byapplying 5 different heating elements to an aluminum plate havingdimensions of 100 mm×100 mm×10 mm. TABLE 2 Thermally ProtectiveProduction insulating Resistive layer Sample method layer circuit(monolayer) 1 According made of made of made of to FIG. 4 ZrO₂—MgO brasssilicon Thickness Thickness Thickness 250 μm 30 μm 50 μm 2 Accordingmade of made of made of to FIG. 3 ZrO₂—MgO tungsten ZrO₂—MgO Thicknessmixed with Thickness 250 μm ZrO₂—MgO 50 μm Thickness 100 μm 3 Accordingmade of made of made of to FIG. 6 ZrO₂—MgO copper ZrO₂—MgO ThicknessThickness Thickness 250 μm 100 μm 50 μm 4 According made of made of madeof to FIG. 6 ZrO₂—MgO tungsten ZrO₂—MgO Thickness Thickness Thickness250 μm 100 μm 50 μm 5 According made of made of made of to FIG. 5ZrO₂—MgO copper ZrO₂—MgO Thickness Thickness Thickness 250 μm 100 μm 50μm

The thickness of the thermally insulating layer indicated in Table 2 isa total thickness, i.e. it includes the thickness of the interlayer.

The dimensions of the electrically resistive circuit were the same forall the samples (as described in Example 1) except for sample 2 whichpresented a very simple circuit design comprising only 5 verticalheating branches 23 a having a width of about 18 mm and being spacedfrom each other of about 4 mm.

Said samples 1-5 were firstly subjected to three thermal cycles byheating them up to 200° C. by introducing them into an air oven. All thesamples successfully passed the test remaining undamaged.

Subsequently, said samples were connected to a current generator and thefollowing measurement were carried out as indicated in Tables 3 and 4.TABLE 3 Electrical Resistive Power resistance circuit supplied byHeating of the surface the rate circuit area generator Sample (° C./min)(Ω) (cm²) (W) 1 26.1 4.6 92 126 2 9.4 12 110 85 3 27.4 1.8 82 144 4 8.314.1 82 73 5 10.0 3.2 84 80

TABLE 4 Normalized Surface area of the heating rate resistive circuit/Sample (° C./min)/(W/cm²) total surface area 1 19.1 0.66 2 12.2 0.76 315.6 0.66 4  9.4 0.66 1 10.5 0.66

The term “Resistive circuit surface area” indicates the surface area ofthe sample within which the resistive circuit is contained.

The ratio “Surface area of the resistive circuit/total surface area”indicates the percentage of the resistive circuit surface area which isactually occupied by the resistive circuit.

The heating rate was measured by using a thermocouple contacting theouter surface of the heating element.

The normalized heating rate indicates the heating rate in respect of thepower supplied by the generator (said power varies from sample to samplesince it depends on the electrical resistance of the resistive circuit)and of the surface area of the resistive circuit. Therefore, the highestis the value of the normalized heating rate, the most efficient is theheating element in terms of heat amount transferred to the outer surfaceof the sample.

The value of the ratio between the surface area of the resistive circuitand the total surface area indicates how the obtained heat amount isdistributed on the outer surface of the heating element. Therefore, thehighest is the value of said ratio, the most uniform is the distributionof the obtained heat amount.

From the data shown in Tables 3 and 4 it can be pointed out that to thesuperior performance of sample 1 contributes the very low thickness ofthe outermost protective layer.

It can also be pointed out that sample 2, despite its very simplecircuit design, produces remarkable results in terms of heating amounttransferred to the outer surface of the sample.

EXAMPLE 3

The heating element C described in Example 1 was used to evaluate theprecuring of a rubber sheet sample.

Said rubber sheet, having a thickness of 2 mm, was positioned to coverthe heating element C and a weight of about 600 g was positioned ontosaid rubber sheet in order to ensure a good contact between the latterand the outer surface of the heating element.

An electrical current of 5.3 A and 24 V was made to flow into theelectrically resistive circuit of the heating element until athermocouple contacting said heating element reached a temperature of200° C.

Subsequently, the rubber sheet was removed from the heating element andcooled down to the room temperature.

In order to evaluate if the precuring of the rubber sheet was occured,the latter and the green rubber sheet were subjected to ultimate tensilestress, ultimate elongation and stress at break at 100% elongation (CA1testings according to Standard UNI ISO 9026. The results are summerizedin Table 5. TABLE 5 Green rubber Rubber sheet Sample sheet after coolingUltimate tensile 0.03 0.1 stress (MPa) Ultimate 800 472 elongation (%)CA1 0.23 0.30 (MPa)

As indicated in Table 5, the increasing of CA1 as well as the decreasingof the ultimate tensile stress and of the ultimate elongation indicatethat the rubber sheet was precured.

Furthermore, the rubber sheet after cooling was longitudinally cut intotwo pieces, each having a thickness of 1 mm, so as to form a bottomrubber sheet (which contacted the heating element during the heatingprocess) and a top rubber sheet (not in contact with the heating elementduring said heating process). The testings mentioned above were carriedout on said two rubber sheets and the result are summerized in Table 6.TABLE 6 Bottom Top Sample rubber sheet rubber sheet Ultimate tensile0.12 0.10 stress (MPa) Ultimate 323 417 elongation (%)

The data from Table 6 indicate that a gradient of curing was present inthe rubber sheet and, in more details, that the bottom rubber sheet wasmore cured than the top rubber sheet.

The present invention presents a plurality of advantages.

First of all the toroidal support according to the present invention,being heated only in correspondence of its outer surface thanks to theheating element described above, allows that the whole body of thetoroidal support has not to withstand repeated thermal cycles whichinevitably subject the support material to thermal fatigue. Therefore,the life of the toroidal support is advantageously increased and, at thesame time, a remarkable energy saving is obtained since the heating ofthe whole body of the toroidal support is remarkably reduced.

Furthermore, the toroidal support according to the present inventionallows a very fast heating of the inner circumferential surface of thegreen tyre as well as a homogeneous heat distribution on the outersurface of the toroidal support since a very high surface area thereofis covered by the resistive circuit.

Furthermore, the heating element provided to the toroidal supportallows, if necessary, a local distribution of the heat amount so thatportions of the toroidal support can be differently heated from eachother. Said aspect is particularly advantageous for instance in the casethe heating element provided to the toroidal support is used not onlyfor precuring the tyre liner, but also during the vulcanization step incombination with the traditional heat amount provided by thevulcanization fluid as well as through the walls of the moulding cavity.Generally, since the tyre to be vulcanized is positioned inside of themoulding cavity with its sidewalls substantially parallel to the base ofthe vulcanizer, the condensate that forms during the curing stepaccumulates in correspondence of the lower sidewall of the tyre so thatsaid lowe sidewall reaches a temperature, and thus a curing degree,lower than that of the upper sidewall. In order to avoid such adrawback, according to the present invention a locally heat distributionof the toroidal support can be carried out so that the lower sidewallcan be heated more that the upper one.

Furthermore, the toroidal support according to the present invention issimple to be obtained, the heating element provided to the support beingof reduced volume and rather easy to be repaired.

1-33. (canceled)
 34. A process for manufacturing a tyre, comprising:providing an elastomeric layer on an outer surface of a toroidalsupport; manufacturing the tyre on the toroidal support provided withthe elastomeric layer; introducing the tyre supported on the toroidalsupport into a moulding cavity; introducing a fluid under pressure intoa space defined between the toroidal support and an inner surface of thetyre in order to press an outer surface of the tyre against walls of themoulding cavity; and curing the tyre; wherein the outer surface of thetoroidal support comprises a shape substantially matching a shape of theinner surface of the tyre, wherein the elastomeric layer forms an innercircumferential surface of the tyre, wherein the walls of the mouldingcavity comprise a shape that matches a shape of the outer surface of thetyre, and wherein the process further comprises causing an electricalcurrent to flow in at least one heating element provided to the outersurface of the toroidal support so as to obtain at least partialprecuring of the elastomeric layer.
 35. The process of claim 34, whereincausing the electrical current to flow in the at least one heatingelement is carried out before introducing the fluid under pressure. 36.The process of claim 34, wherein causing the electrical current to flowin the at least one heating element is carried out after providing theelastomeric layer on the outer surface of the toroidal support.
 37. Theprocess of claim 34, wherein causing the electrical current to flow inthe at least one heating element is carried out after manufacturing thetyre on the toroidal support.
 38. The process of claim 34, whereincausing the electrical current to flow in the at least one heatingelement is carried out before providing the elastomeric layer on theouter surface of the toroidal support.
 39. The process of claim 34,wherein causing the electrical current to flow in the at least oneheating element is carried out during curing the tyre.
 40. The processof claim 34, wherein at least a portion of the outer surface of thetoroidal support is selectively heated.
 41. The process of claim 34,wherein the electrical current comprises direct current, alternatecurrent, pulsating current, or waveform current.
 42. The process ofclaim 34, wherein the intensity of the electrical current is controlled.43. The process of claim 34, wherein the at least one heating elementcomprises: a thermally insulating layer; and an electrically resistivecircuit.
 44. The process of claim 43, wherein the thermally insulatinglayer is obtained by using a plasma-spray technique.
 45. The process ofclaim 43, wherein the electrically resistive circuit is obtained byusing a plasma-spray technique.
 46. A toroidal support for manufacturinga tyre, comprising: a plurality of circumferential segments defining anouter surface of the toroidal support; wherein the outer surface of thetoroidal support comprises a shape substantially matching a shape of aninner surface of the tyre, wherein the toroidal support furthercomprises at least one heating element covering at least a portion ofthe outer surface of the toroidal support, and wherein the at least oneheating element comprises, in a radial direction from an inside towardan outside of the at least one heating element, a thermally insulatinglayer and an electrically resistive circuit.
 47. The toroidal support ofclaim 46, wherein the thermally insulating layer is made of ceramicmaterial.
 48. The toroidal support of claim 47, wherein the ceramicmaterial is: a mixture of zirconium dioxide and magnesium oxide(ZrO₂—MgO), aluminum oxide (Al₂O₃), a mixture of aluminum oxide andtitanium dioxide (Al₂O₃—TiO₂), or a mixture of zirconium dioxide andtitanium dioxide (ZrO₂—TiO₂).
 49. The toroidal support of claim 46,wherein the thermally insulating layer has a thickness greater than orequal to 0.02 mm and less than or equal to 1 mm.
 50. The toroidalsupport of claim 46, wherein the electrically resistive circuitcomprises a plurality of heating branches.
 51. The toroidal support ofclaim 46, wherein the electrically resistive circuit is made of anelectrically conductive material.
 52. The toroidal support of claim 51,wherein the electrically conductive material is a metal or metal alloy.53. The toroidal support of claim 51, wherein the electricallyconductive material is copper, tungsten, or an aluminum alloy.
 54. Thetoroidal support of claim 51, wherein the electrically conductivematerial has an electrical resistivity greater than or equal to 1.7×10⁻⁶Ω×cm and less than or equal to 1.1×10⁻⁴ Ω×cm.
 55. The toroidal supportof claim 46, wherein the electrically resistive circuit has a thicknessgreater than or equal to 0.01 mm and less than or equal to 0.5 mm. 56.The toroidal support of claim 46, wherein the at least one heatingelement further comprises a protective layer radially external to theelectrically resistive circuit.
 57. The toroidal support of claim 56,wherein the protective layer is made of ceramic material.
 58. Thetoroidal support of claim 56, wherein the protective layer is made ofTEFLON®.
 59. The toroidal support of claim 56, wherein the protectivelayer comprises at least two layers.
 60. The toroidal support of claim59, wherein one of the at least two layers is a thermally insulatinglayer.
 61. The toroidal support of claim 46, wherein one or more of thecircumferential segments is provided with the at least one heatingelement.
 62. The toroidal support of claim 46, wherein at least one ofthe circumferential segments is provided with a heating elementcomprising at least two electrically resistive circuits.
 63. Thetoroidal support of claim 62, wherein the at least two electricallyresistive circuits are selectively heated.
 64. The toroidal support ofclaim 62, wherein the at least two electrically resistive circuitscomprise different geometrical configurations.
 65. The toroidal supportof claim 62, wherein the at least two electrically resistive circuitscomprise heating branches with different densities of the heatingbranches.
 66. The toroidal support of claim 46, wherein the electricallyresistive circuit comprises heating branches with different densities ofthe heating branches.